Although interleukin-8 (IL-8) is a chemokine that plays a beneficial and central role in the inflammatory response, hematopoiesis, and angiogenesis, excessive IL-8 production can be deleterious to the host, and its selective inhibition represents an important therapeutic goal. Vasoactive intestinal peptide (VIP) is a neuropeptide that acts as a potent anti-inflammatory agent inhibiting the function of activated macrophages/monocytes. The present study reports the effect of VIP on IL-8 production by stimulated human THP1 monocytes. VIP inhibits IL-8 production in a dose- and time-dependent manner at the mRNA level. VIP seems to act by inhibiting the NF-kappaB-dependent IL-8 gene activation. The specific VPAC1 receptor mediates the inhibitory effect of VIP. Two transduction pathways appear to be involved, a major cAMP-independent pathway that preferentially blocks nuclear translocation of NF-kappaB and its binding to the kappaB site of the IL-8 promoter, and a cAMP-dependent pathway that inhibits the activation and binding to the IL-8 promoter of both CREB-binding protein (CBP) and TATA box-binding protein (TBP), two transcriptional cofactors strictly required for the transactivating activity of NF-kappaB. These findings support the proposed role of VIP as a key endogenous anti-inflammatory agent and describe a novel mechanism, i.e., the inhibition of the production of monocyte-derived IL-8, and are of obvious physiological significance, because VIP, through the inhibition of IL-8 production, could reduce the monocyte-induced neutrophil chemotaxis/infiltration, an important event in the pathogenesis of several inflammatory and autoimmune disorders.